The present invention relates to a low IF (Intermediate Frequency) receiver and method thereof, and more particularly to a large SNR (Signal-to-noise Ratio) wireless receiver and method thereof.
In a wireless communication system, a low IF (Intermediate Frequency) receiver is employed to receive a radio frequency (RF) signal, wherein the RF signal is down-converted into a low (but non-zero) frequency signal such that the low frequency signal is capable of being processed by the following circuits of the receiver. Furthermore, the low IF receiver possesses the advantages of small DC offset and low flicker noise. However, the non-zero down-converted signal may induce some image in the output of the low IF receiver. Conventionally, an image rejection filter is utilized to filter out (i.e., to reject) the image band signal, wherein the image rejection filter is placed between a low-noise amplifier and a down-converted mixer of the receiver. In other words, the image rejection filter is operated under the RF band since the image rejection filter is placed before the down-converted mixer in the receiver. Therefore, the quality factor (i.e., Q factor) of the components composing the image rejection filter should be high enough to meet the required performance of the image rejection filter. One of the solutions is to place the image rejection filter externally, i.e., utilizing an off-chip image rejection filter to reject the RF image band. However, the cost of the off-chip components composing the off-chip image rejection filter may be too high for the receiver. Furthermore, the large area occupied by the off-chip image rejection filter is another problem faced by the conventional art. Therefore, providing a high quality low IF receiver at a low cost that occupies a small area is a significant concern in the wireless communication field.